No effective cure has yet been found for loss of sight in spite of recent development in medical technique. Loss of sight is not only a mere obliteration of visual function but also it affects a patient's spiritual life and social life. Accordingly, a technique for curing the loss of sight has been desired.
FIG. 1 is a sectional view of a retina. A sclera A forming an outer layer of an eyeball is outside a retina. Inside the sclera are photoreceptors B, retinal bipolar cells C and retinal ganglion cells D sequentially in this order. Of these, the photoreceptors B serve to receive light and convert it to an electric signal. The retinal bipolar cells C and retinal ganglion cells D serve to transmit the electric signal to the brain. Light incident in front of the eyeball (from downward in the figure) passes through the transparent retinal ganglion cells D and retinal bipolar cells C to be sensed by the photoreceptors B and converted to an electric signal. Thereafter, the electric signal is transmitted through the retinal bipolar cells C to the retinal ganglion cells D. Distal ends of the retinal ganglion cells D extend into the brain, and the electric signal forms an image in the brain.
FIG. 2 is a sectional view of a conventional electrode member for retinal stimulation 100 (hereinafter referred to as “electrode member 100”) attached over a retina. The electrode member 100 is connected to one end of an electric wire 104 there to transmit, to the retinal bipolar cells C, an electric signal for an image transferred from the other end (not shown) of the electric wire. The electrode member 100 is provided with a plurality of electrodes 101 transmitting an electric signal, a support 102 holding the electrodes 101 at a predetermined location (for example, in a matrix) and a fixing pin 103 for fixing the support 102 to the sclera A. Each electrode 101 is provided so as to be exposed flat on the underside (side in contact with the retina) of the support 102.
However, when the fixing pin 103 is inserted into the sclera A so that the electrode member 100 is fixed over the retina, the support 102 is sometimes depressed against the retina more than necessary. In this case, since the electrode member 100 is fixed over the retina while the overall underside of the support 102 is in contact with the retina, there is a possibility that the underside of the support may press the retina, adversely affecting the retina.
Furthermore, although a portion to which the electrode 101 originally supplies the electric signal is the retinal bipolar cells C, the conventional electrode member 100 has such a structure that the electric signal is also supplied to the retinal ganglion cells D as well. The retinal ganglion cells D extend into the shape of a stalk in order to transmit electric signals from a plurality of the retinal bipolar cells C. Accordingly, for example, as shown in FIG. 3, even when voltage corresponding to an image of character “H” (voltage is applied to the electrodes 101 indicated by “+”) is applied in the case of the electrode member 100 provided with 36 electrodes 101, the user (a sightless person) sometimes recognizes it as an image of character “U.”
The present invention was made in view of the foregoing circumstances, and an object thereof is to provide an electrode member for retinal stimulation which can form an actually transmitted image without pressing the retina in an excessively broad range.
Furthermore, another object is to provide an artificial retina device which can transmit an image signal into the brain using the electrode member.